568 PROCEEDINGS OF THE SOCIETY". 



a great change in this respect. It was a moot point whether the ether 

 was of the same density throughout the universe. If not, cadmium 

 would be as little permanent as a standard as would platino-iridium, which 

 was now being used. Therefore the measuring of those standards in 

 wave-lengths only possessed the value of giving us another independent 

 and supposed-to-be constant standard. There was evidence that standards 

 were much the same now as they used to be. With regard to the 

 standard yard, he doubted very much whether the work carried out by 

 the Board of Trade to measure the standard yard was worth the money 

 spent on it, especially on a basis of wave-length. It was already known 

 that the yard was either growing or getting less — he did not remember 

 which — all the time. In the different measurements which had been 

 made it was found to have changed considerably, and no doubt it was 

 changing now, and probably would go on changing for ever, or as long 

 as it escaped another fire like that in the House of Parliament 100 years 

 ago. He did not see what was the real interest of such minute measure- 

 ments as those just demonstrated. It seemed to him very much like 

 measuring a puppy dog to the T ^ in. one day, and finding the next day 

 it had grown. 



Mr. Beck, in reply, said it would be interesting to hear what would 

 be said at the Royal Society meeting on the following evening, because 

 he believed that the standard which was to be discussed there was one 

 made of fused quartz. The Board of Trade had tried making various 

 measurements with crystalline quartz, but had found that it was not stable. 

 It was supposed that fused quartz was more likely to be stable than 

 anything else. He was told that even platino-iridium was not above 

 suspicion, and it was hoped that fused quartz would constitute a less 

 variable standard than anything which had hitherto been suggested. 

 What Mr. Conrady said about micrometers was true, provided we knew 

 they were correct, but he thought actual measurement of a certain 

 number was important, so that one might know whether they were any- 

 where near correct ; because when it came to subdividing anything as 

 large as a metre or a yard down to t -Jq mm., so many errors might 

 creep in that microscopists would be more satisfied if they could be 

 assured that one or two specimens were approximately accurate. If 

 they were found to be accurate, one might well leave the question of 

 accuracy to one part in a million to those who were sufficiently interested 

 to make careful experiments. But he thought it important that some 

 stage-micrometers should be measured on the method which he had set 

 out, which was certainly the most delicate method of measurement 

 known, in order to satisfy ourselves that the measurements were within 

 the ordinary range of accuracy which was required. He believed it was 

 true that the original standard yard was changing very slightly, though 

 one might almost derive the impression from Mr. Conrady's remarks 

 that it was changing at a rapid rate and by a considerable amount. He 

 (Mr. Beck) believed that the change was extraordinarily minute. The 

 standard, which, he believed, was only taken out of its hiding-place once 

 in twenty years, was compared with platino-iridium and other standards 

 from time to time ; and he believed the Standards Office had in their 

 possession standards made of different materials, which were periodically 

 compared in order to ascertain what was, at all events, the relative vari- 

 ation in the metals. In discussing the question of the influence of the 



